Conventionally, a laminate including a layer of a polyolefin resin such as a polyethylene or a polypropylene and a layer (hereinafter sometimes abbreviated as “EVOH layer”) of a saponified ethylene-vinyl acetate copolymer (hereinafter sometimes abbreviated as “EVOH”) excellent in gas barrier property is formed into films, sheets, cups, trays, bottles and the like, which are commercially used for various applications with the advantageous properties of the laminate and, particularly, employed as packaging materials for foods and drugs. When the aforementioned products are formed from the laminate including the polyolefin resin layer and the EVOH layer, a waste material such as debris and end margins, and defective products occur. Further, refuses of the formed products occur after use in various applications. These scraps account for 50 to 30% (area percentage) of the original laminate. Therefore, the scraps are recycled to be melt-formed into a recycle layer (which is a so-called regrind layer and, in the present invention, sometimes referred to as “regrind layer”) serving as at least one layer of a laminate. The recycling technique is industrially useful for reduction of industrial wastes and for economy, and employed in practical applications.
However, the compatibility between the polyolefin resin and the EVOH is poor. Therefore, when a scrap laminate including the polyolefin resin layer and the EVOH layer is re-melted to be reused as a material for a regrind layer, the polyolefin resin and the EVOH are not properly mixed with each other. Accordingly, a phase-separation product is liable to occur (die build-up), and is often incorporated in a formed product. This results in formation of fish eyes and holes in the formed product and formation of wave patterns on a surface of the formed product.
A known technique for ameliorating the compatibility that is the caused for the die build-up and the poor appearance is to blend a saponified ethylene-vinyl acetate copolymer having a higher ethylene content (see Patent Documents 1 to 3).
The ethylene-vinyl acetate copolymer is herein abbreviated as EVA. The EVA saponification product having higher ethylene content as identified above is highly compatible with polyolefins. More specifically, the higher ethylene content EVA saponification product is an ethylene-vinyl acetate copolymer saponification product having an ethylene content of not less than 70 mol %.
On the other hand, the EVOH is an ethylene-vinyl acetate copolymer saponification product (EVA saponification product) having an intermediate ethylene content and excellent in gas barrier property. More specifically, the EVOH is an ethylene-vinyl acetate copolymer saponification product having an ethylene content of 10 to 60 mol %.
The inventors of the present invention examined methods disclosed in Patent Documents 1 to 3, and found that these methods are relatively effective in solving the problems associated with the poor compatibility between the polyolefin resin and the EVOH, but lead to a problem such that the resulting regrind layers are colored yellow or red. In order to suppress the coloration, the inventors made an attempt to employ a smaller amount of the higher ethylene content EVA saponification product. However, the compatibilizing effect is impaired, so that the problems associated with the compatibility (the die build-up and the poor appearance) are insufficiently solved.
On the other hand, a resin composition which includes a base resin containing an EVA and a higher ethylene content EVA saponification product is proposed as a modifier for improving the compatibility in the regrind layer (see Patent Document 4). Even with the use of this resin composition, the problem associated with the coloration is yet to be solved.
Patent Document 1: JP-A-HEI3 (1991)-215032
Patent Document 2: JP-A-HEI3 (1991)-72542
Patent Document 3: JP-A-HEI3 (1991)-72539
Patent Document 4: JP-A-2002-234971